Yes, you must run the output voltage to a voltage divider. The output voltage will rise higher than supply +. You must not let the pic be exposed to a level greater than specs permit.
Or it is typical to use a sense resistor somewhere.
Such as:
The sense resistor should have a low ohm value, yet which is just high enough to develop a usable volt reading for the pic.
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Your On time might be a variable named 'Duty_On'.
The Off time might be 'Duty_Off'.
Set a counter to zero. Pull the bias control pin high. Go through a repeating loop, incrementing the counter each time. When the counter reaches Duty_On, exit the loop. (As an alternate, use the pic's onboard timer variable.)
Set the counter to zero. Pull the bias control pin low. Go through a repeating loop, incrementing the counter each time. When the counter reaches Duty_Off, exit the loop.
After going through the above loops a few times, read the sense resistor. If sensed V is high, reduce Duty_On. If sensed V is low, increase it.
As for Duty_Off, you may want to increase it or decrease it correspondingly.